The present invention relates to the art of medical diagnostic cardiac imaging. It finds particular application in conjunction with computed tomography (CT) scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications including other imaging modalities, such as, e.g., magnetic resonance imaging (MRI), electron beam CT (EBCT), etc.
Cardiac imaging is an important application for medical diagnostic imaging. Presently, there are a number of different imaging modalities which address the task, such as, e.g., CT, MRI, and the like. The goal is to image the heart at any selected one or more of the multiple phases of the cardiac cycle. This allows visualization of the coronary arteries for coronary artery disease, wall motion abnormalities, valve abnormalities, and other pathology. It is, therefore, desirable to identify accurately the different phases of the heart which have physiologic significance, and, to be able to identify these phases as the heart rate for a given patient varies, and also for different patients varying in age, gender, and physical condition.
Accordingly, in a preferred embodiment, one purpose of the present invention is to provide for an algorithm/model, and an apparatus for implementing the same, that uses the heart rate to automatically calculate or otherwise determine the different phases of the heart as the heart rate of the patient being imaged changes. Moreover, the approach is optionally used for identifying multiple phases accurately across a differing patient population. Alternatively, another specific application is to identify that point in the cardiac cycle when the heart is most stationary. Imaging of the heart at this point minimizes motion artifacts otherwise generated, and, in turn, results in superior visualization of the heart.
Typically, previous developed methods use a fixed absolute delay or alternately a fixed percentage delay from a readily pinpointed time in the cardiac cycle (e.g., the R wave in the electrocardiogram (ECG) waveform) to identify or determine when the heart is at a given phase in the cardiac cycle. However, when these approaches are extended to generating images of multiple phases, it leads to dividing the cardiac cycle into equal parts. Because of the complex motion of the heart different parts of the heart cycle are affected differently with variations in the heart rate. That is to say, e.g., at progressively faster heart rates the diastole portion of the heart cycle becomes progressively shorter in length while the systole portion remains largely unchanged. Consequently, using a fixed delay (either an absolute delay or a percentage of the cardiac cycle) is not sufficiently adapted to locating the same desired phase from cycle to cycle when a patient has a dynamically changing heart rate during the scan. This approach becomes even more difficult when used across populations of patients having differing physiological characteristics. Further difficulties are encountered when fixed delay cardiac imaging is undertaken using an imaging apparatus having longer acquisition times and more stringent temporal demands (e.g., conventional CT scanners).
Accordingly, the present invention contemplates a new and improved technique for cardiac imaging which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method of cardiac gating for use in an imaging apparatus is provided. The method includes monitoring a patient""s cardiac cycle, and determining a cardiac cycle time for the patient. A desired cardiac phase of interest is selected, and a delay from a reference point in the cardiac cycle is determined. The delay is a function having a nonlinear relationship with respect to at least one of the selected cardiac phase and the cardiac cycle time. Finally, the selected cardiac phase is located in the cardiac cycle using the delay.
In accordance with another aspect of the present invention, a medical diagnostic imager includes an imaging apparatus which scans a patient to acquire image data from the patient. An image processor receives the image data from the imaging apparatus and reconstructs therefrom an image representation of the patient. Also included is a rendering engine which provides the image representation in a human-viewable format. Cardiac gating means control at least one of the imaging apparatus and the image processor such that the image representation obtained coincides with a desired cardiac phase of the patient. The cardiac gating means compensates for nonuniform changes in the patient""s cardiac cycle corresponding to a nonuniform distribution of cardiac phases in the patient""s cardiac cycle.
One advantage of the present invention is accurate positioning of an acquisition window to image one or more desired phases of the heart.
Another advantage of the present invention is compensation for motion artifacts in cardiac images.
Yet another advantage of the present invention consistent identification and imaging of the same desired heart phase from cycle to cycle in a patient having a dynamically changing heart rate during the imaging scan.
Another advantage of the present invention is its generality for use with multiple image modalities, and its adaptability for use with patients having differing physiologies.
Another advantage of the present invention is that accuracy and repeatability is achieved when more than one phase of the heart is being imaged.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.